Re: [PATCH 1/2] blk-mq: not deactivate hctx if the device doesn't use managed irq
flat view
From: Hannes Reinecke <hare@suse.de>
Date: 2021-06-29 12:39:19
Also in:
linux-nvme
On 6/29/21 9:49 AM, Ming Lei wrote:
hctx is deactivated when all CPU in hctx->cpumask become offline by draining all requests originated from this hctx and moving new allocation to active hctx. This way is for avoiding inflight IO when the managed irq is shutdown. Some drivers(nvme fc, rdma, tcp, loop) doesn't use managed irq, so they needn't to deactivate hctx. Also, they are the only user of blk_mq_alloc_request_hctx() which is used for connecting io queue. And their requirement is that the connect request can be submitted via one specified hctx on which all CPU in its hctx->cpumask may have become offline.
How can you submit a connect request for a hctx on which all CPUs are offline? That hctx will be unusable as it'll never be able to receive interrupts ...
quoted hunk ↗ jump to hunk
Address the requirement for nvme fc/rdma/loop, so the reported kernel panic on the following line in blk_mq_alloc_request_hctx() can be fixed. data.ctx = __blk_mq_get_ctx(q, cpu) Cc: Sagi Grimberg <sagi@grimberg.me> Cc: Daniel Wagner <redacted> Cc: Wen Xiong <redacted> Cc: John Garry <redacted> Signed-off-by: Ming Lei <redacted> --- block/blk-mq.c | 6 +++++- include/linux/blk-mq.h | 1 + 2 files changed, 6 insertions(+), 1 deletion(-)diff --git a/block/blk-mq.c b/block/blk-mq.c index df5dc3b756f5..74632f50d969 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c@@ -494,7 +494,7 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q, data.hctx = q->queue_hw_ctx[hctx_idx]; if (!blk_mq_hw_queue_mapped(data.hctx)) goto out_queue_exit; - cpu = cpumask_first_and(data.hctx->cpumask, cpu_online_mask); + cpu = cpumask_first(data.hctx->cpumask); data.ctx = __blk_mq_get_ctx(q, cpu);
I don't get it. Doesn't this allow us to allocate a request on a dead cpu, ie the very thing we try to prevent? Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer